This invention relates to novel fluorinated organosilicon compounds useful as a crosslinking agent in addition reaction.
Rubber compositions of the addition reaction curing type generally contain a base polymer having alkenyl radicals such as vinyl, a compound having at least three hydrogen atoms directly attached to silicon atoms (i.e., SiH radicals), and an addition reaction catalyst such as platinum catalyst. The compositions cure through addition reaction of SiH radicals to alkenyl radicals on the base polymer.
Known fluorinated organosilicon compounds having SiH radicals include those compounds of the structure wherein three SiH radicals are attached via oxygen atoms to a Si atom having a fluoroalkyl substituent radical as shown below (JP-A 3-197484). 
By virtue of fluoroalkyl radicals, these compounds are compatible with base polymers having high fluorine contents. They are very useful as a crosslinking agent particularly when combined with base polymers in the form of terminally modified perfluoropolyether.
Physical properties of cured rubber compositions of the addition reaction curing type, especially hardness and modulus are governed by the molecular weight of the base polymer and the number per molecule of SiH radicals in the crosslinking agent. As long as the same base polymer is used, the use of the above-mentioned compounds as a crosslinking agent always results in cured rubbers having a limited range of hardness and modulus.
An object of the invention is to provide a fluorinated organosilicon compound having at least four SiH radicals which is highly compatible with base polymers having high fluorine contents.
We have found that fluorinated organosilicon compounds containing fluoroalkyl radicals and at least four SiH radicals per molecule as represented by the formula (1) below are obtained by co-hydrolysis of a trichlorosilane having a fluoroalkyl substituent radical and dimethylchlorosilane, and that these fluorinated organosilicon compounds are highly compatible with base polymers having high fluorine contents.
The invention provides a fluorinated organosilicon compound of the following general formula (1). 
Herein R is independently xe2x80x94(CH2)a-Rf wherein Rf is a monovalent perfluoroalkyl or perfluorooxyalkyl radical having 1 to 12 carbon atoms, and xe2x80x9caxe2x80x9d is 2 or 3, X is xe2x80x94OSi(CH3)2H, and n is 0 or 1.